Effects of clothing on running physiology and performance in a hot condition

Abstract

Distance running, more than any other sport, is etched with the tragedy of heat-related deaths. Clothing as a uniform required in formal competitions satisfies a variety of purposes for athletes during exercise, as it serves as a barrier between skin surface and ambient environment. Clothing plays a vital role in addressing the health and performance of distance runners. In a hot and humid environment, appropriate clothing with improved pattern design and fabric materials can increase the capability of heat dissipation (CHD) from the body to the outer environment. It also helps the body to improve subjective sensations and physiological responses to heat stress, and subsequently affect overall wearing comfort and exercise performance. The aim of this study was to develop a method in designing running clothes to improve the athletes' running performance and wearing comfort in a hot condition, and establish an evaluation system that can be used to quantify the functional performance of developed clothing and to assess the influence of the clothing on athletes' whole-body/local thermal responses, running performance and wearing comfort during running. In this thesis, a theoretical framework was established for developing functional running clothes by studying and identifying the thermal requirements of different body parts. Thermal zones of the human body were specified according to the summary of regional skin temperature and sweat evaporative distribution. Each thermal zone was marked with the specific demands on pattern design and the selection of fabric materials to fulfill the thermal physiological requirements. This helped in developing a new design methodology for summer running clothes, which aimed at increasing the heat dissipation efficiency of clothing and improving the running performance of the athletes. Two types of running clothes with a thermal mapping-designed concept were manufactured based on the newly developed methodology. An evaluating system was developed that can be used to quantify the functional performance of thermal mapping-designed clothing. This system includes three aspects: basic tests on fabric physical properties, assessment of whole clothing properties, and determination of physiological/psychological effects on the human body. The basic tests of fabric physical properties were conducted following existing measurement standards. For the mapping-designed aspect, the clothing properties were calculated according to the physical properties of the fabric and each of its covered area portion. Furthermore, three new indices related to human body's thermal and moisture dissipation via clothing were defined to simulate the overall CHD when the clothing is worn. The overall CHD of clothing is composed of the Capability of Dry Heat Loss (CDHL) and Capability of Latent Heat Loss (CLHL), which were evaluated by a manikin test and calculating methods respectively. The physical properties of the mapping-designed running clothes were evaluated using this system. Evaluation results show that the overall CHD of mapping-designed clothing (CloA) increased by 11%, while that of CloB was at 7% as compared to existing commercial clothing. This proves that clothing designed with mapped patterns and specified functional properties of materials according to the thermal requirements in each body part has positive influence on the overall CHD. The evaluation methods for wear trials, including the experimental design, methodology, and measuring instruments, were discussed for investigation on human body. A parallel-blinded wear trial with a 45 min steady-state running protocol followed by a 1.5 km time trial was conducted. The trial aimed to investigate and verify the effects of mapping-designed running clothes on whole-body thermal responses and running performance on human subjects in a hot condition, and examine the relationships among clothing overall performances, whole-body thermal responses and the time of running performance. The experiments were conducted in a completely controlled heat-conditioned chamber. Subjects were eight endurance male athletes tasked to complete the three tests at random, which was carried out in separated week. The subjects wore one kind of clothing in each test. Findings showed that the clothing designed with an increased CHD by altering design pattern and fabric materials resulted in decreased skin temperature (Ts), less heat storage (S) and delayed increasing of core temperature (Tc) during the rest and steady-state running periods in a hot condition, which were related to the time of performance running (PR) of 1.5km-sprint (P < 0.05). The changes of thermal responses and PR were correlated with the physical properties of clothing (P < 0.05). Specifically, WVPt and OMMCt of clothing, which affect the CLHL, have negative relationships with S, {439}Tc, and PR. The clot and ARt relating to the CDHL has a positive effect on S at 30 min rest and during running performance. Besides, Tc and Ts at the time point of Running End can be predicted by the overall capability of dissipate heat (CHD), as well as the d and the Wt of the clothing. The PR can be directly predicted by the CLHL through the clothing. The effects of mapping-designed running clothes on local thermal responses of athletes were investigated in a wear trial, and the relationships with whole-body thermal responses and running performance were studied. Findings showed that the defined body thermal zone of human body had different thermal responses during the tests, with some responses correlated to the whole-body thermal responses at different exercise statuses and running performance (P < 0.05). Subsequently, the potential mechanism on how the mapping-designed clothing affected the thermal responses and running performance were explored. To sum up, the higher capacity of heat dissipation of the fabric and/or the whole clothing, the less the heat stored in the body and slower increases of Tc, hence inducing less adverse impact of clothing on the running performance while running in a hot condition. The effects of mapping-designed running clothes on subjective sensations and athletes{174} wearing comfort were examined, and the relationships between clothing properties and each sensory factor at different time points were explored. Findings revealed that the specially designed running clothes increased overall wearing comfort and satisfied the related subjective sensations such as coolness, smoothness, and lightness at different exercise statuses (P < 0.05). Five sets of a predictable model were constructed to predict the overall comfort by the four sensory factors at each time point. The agreements between the real comfort sensation obtained from the questionnaire and the predicted comfort by the models were observed respectively with the R2 from 0.47 to 0.57 at each time point, except that at Recovery 30 min. Besides, a factor analysis was conducted to identify the main sensory factors of wearing comfort, some of which were tended to correlate to PR. The finding indicated that these sensation factors could not only predict the overall clothing comfort, but might also have some effects on running performance in a hot condition. In summary, a functional design model and a related evaluating system for thermal mapping-designed running clothes were developed scientifically and systematically in this study. The effect of clothing designed on human responses while running in a hot condition and their mechanisms were examined based on evaluating system. These findings would contribute to the sportswear industry and the field of sports by developing a scientific understanding on the management of heat stress and the improvement of exercise performance with clothing. The results can also enhance the application of sports science in textile industry and provide practical scientific guidelines, technical suggestions, and evaluation systems for product optimization and promotion of sports clothing.